In Nature Biotechnology this week, Massachusetts General Hospital researchers report on a technique for obtaining greater nuclease specificity with the gene-editing tool CRISPR. CRISPR works when Cas9 nucleases, directed by guide RNAs, cause double-strand breaks in specific DNA sequences. However, these nucleases can cause mutations at sites that differ by as many as five nucleotides from their intended targets. To address this, the team used truncated guide RNAs, with regions of complementarity to DNA targets that are less than 20 nucleotides in length. The result was a significant reduction in mutagenesis at off-target sites without a reduction in gene-editing efficiencies.
Meanwhile, in Nature Genetics, a team of Chinese researchers has published the whole-genome sequence of the half-smooth tongue sole — the first flatfish to be sequenced. The investigators sequenced both a male and female of the species, obtaining a view into the structure and evolution of the fish's sex chromosomes that suggests they evolved from a pair of autosomes. GenomeWeb Daily News has more on this fish genome here.